1. Field of the Invention
This invention relates to process for the manufacturer of air bearing sliders including transducers, and more particularly to a process for producing air bearing sliders from a wafer which includes a plurality of transducers.
2. Description of the Prior Art
In the prior art, methods of producing sliders with thin film read/write heads have followed a technique such as that illustrated in U.S. Pat. No. 5,095,613 to Hussinger et al., issued Mar. 17, 1992. The process in Hussinger begins, in one embodiment with a wafer on which a plurality of read/write transducers have been manufactured. From the wafer a row of transducers are sliced and the row is glued to a fixture. Or alternatively, the wafer is glued to a fixture, such as illustrated in the embodiment disclosed in FIG. 7, leaving a row of transducers exposed and available for processing. The row of transducers are all simultaneously lapped to provide the appropriate throat height for the transducers. In a prior art process described and illustrated in Hussinger et al., and more particularly the process of FIGS. 6, 6a and 6b in Hussinger et al., a row of transducers is removed from a wafer and the row of transducers is processes simultaneously. One of the problems with the foregoing processes which utilize a row-processing technique is that because of a bowing of the row of transducers, a non-uniform throat height from end-to-end of the row results. This phenomenon is referred to as row bow. The resulting heads across the row have varying throat heights, which results in magnetic transducers having non-uniform electrical characteristics. The read/write electrical characteristics of a magnetic transducer varies substantially as a result of a variation of throat height and accordingly with a non-uniform throat height of the devices the electrical characteristics of magnetic heads produced by the row processing technique can widely vary. If read/write transducers having a small margin of error from transducer-to-transducer in regard to their electrical characteristics are required, then the variations in the characteristics from transducer-to-transducer produced by the row process may require that a high percentage of the devices be discarded, resulting in unacceptably low yield.
Conventional, row-oriented slider fabrication processes separate by a row at a time sliders which have been formed on the surface of a wafer. For example, referring to FIG. 1, wafer 1 includes a plurality of rows 2 in which heads (not shown) are formed in a alignment across the row. All heads on the row must be colinear, that is oriented in a straight line in order for them to have equal throat heights when the row of heads are processed in a method such as that illustrated in the Hussinger et al. patent. The requirement that all heads in a row be colinear places a constraint on the wafer layout. More particularly, all heads must be arranged in rectangular arrays such that all rows are of equal length for batch processing. If a square wafer is utilized, then the layout is straight forward since the rows may be made the width of the wafer. However, it is preferable to use a round wafer since it is easier to coat evenly with photoresist. As will be appreciated from reference to FIG. 1, the rectangular array constraint results in a significant loss of usable are of the wafer since those areas indicated at 3 will not include heads. Thus this loss of area reduces the number of sliders which may be manufactured per processed wafer, hence increasing the cost of the heads. The unusable area may be as much as 50% of the wafers, total area, resulting in considerable waste. Additionally, this colinearity requirement also places constraints on the wafer-level element fabrication process, especially the photolithography process. When the sliders which are being manufactured utilize thin film heads, 1.times. projection and lithography, and step and repeat lithography are commonly used. Both are affected by the colinearity requirements. For 1.times. projection processes, the mask must be precisely made so that each rows' elements line up within hundredths of a micron, which increases the cost of the mask. Additionally, the distortion of the exposure process must also be tightly controlled.
If a step-and-repeat process is used to define the transducer elements, additional colinearity implications are encountered which are more onerous than those encountered with the precision required for the mask. Alignment between stepped fields is typically only achievable within tenths of a micron. Thus splitting a row across two or more fields can result in a shift in throat height. This is illustrated in FIG. 2 where a highly magnified view of portion 4 of wafer 1 is illustrated. In FIG. 2, in field "n" transducer elements are indicated by circles and the centerline of those elements is indicated by dashed line 5. Similarly, the transducer elements in field n+1 are indicated by circles and the centerline of those elements indicated by dashed line 6. As will be appreciated by reference to FIG. 2, the difference in distance between lines 5 and 6 illustrate the misalignment and lack of colinearity. When the row containing these misaligned portions is processed on the row-basis, an unacceptable variation in throat height will result. One possible solution to this misalignment where a plurality of fields are used in a row is to avoid this by having an entire row contained in a single field. This however limits the size of the row since stepper lithographic fields are limited in size, and therefore limiting the row lengths to the field size can limit the utilization to the wafer. For example, referring to FIG. 3, wafer 7 is illustrated, with the wafer having a plurality of fields indicated at 8. The width of the field (and accordingly the length or the row) is limited by the field size and therefore further inefficiency results since unusable areas 9 are left. The layout in FIG. 3 is not optimum because it requires may more fields to be printed.
An optimum layout would be one such as that illustrated in FIG. 4 in which four fields are utilized to more efficiently cover the surface of wafer 10. The fields in FIG. 4 are denoted by F1, F2, F3 and F4. From the above, it will be appreciated that the processing on a row by row basis makes the stepper lithography less efficient and more expensive.